Recently, a modem having the function of a facsimile machine (hereinafter referred to as a FAX modem) has become popular. The FAX modem is an apparatus for converting documents, drawings or the like prepared by a computer into image data, and then transmitting the image data to a facsimile machine through a telephone line. It is possible for the FAX modem to transmit the document and the drawings etc. prepared by the computer to the facsimile machine without performing printing by a printer. Because there are some errors in reading papers caused by mechanical parts of the facsimile machine when the papers printed by the printer are read by the facsimile machine, the FAX modem has the advantage of no such errors in reading, and is capable of performing data transmission with high accuracy.
There is a demand to use a facsimile machine as a printer when the FAX modem is located near a facsimile machine. In that case, it is feasible to use the facsimile machine as a printer when the image data is transmitted to the facsimile machine by the FAX modem through the telephone line. However, since the data transmission performed therebetween requires the use of the telephone line, it requires various operations in addition to phone charges.
To resolve the problems described above, the applicant has already filed one patent application to the Japanese Patent Office entitled "Network Control Unit" (application number Hei 1-38949 and laid-open publication number Hei 2-218259). The inventions disclosed in the application have come to actual products named "STARFAX" and the products are on the market.
FIG. 1 shows a FAX modem 2 disclosed in laid-open publication number Hei 2-218259. In the FAX modem 2, both a switch 12 and a switch 14 are switched to a contact 12a and a contact 14a respectively, together with switching of a switch 16 and a switch 18, so as to contact 16b and to contact 18b, by controlling a relay 6 utilizing a computer 4. By carrying out these switchings, a facsimile modem circuit 24 (hereinafter referred to as FAX modem circuit) is coupled to a telephone line 22, so that data transmission through the telephone line 22 can be performed.
Also, the switch 12 and the switch 14 are switched to the contact 12a and the contact 14a together with switching of the switch 16 and the switch 18 so as to contact 16b and to contact 18b by controlling the relay 6 utilizing the computer 4. Thus, the facsimile machine 20 and the FAX modem circuit 24 are connected in series so that a voltage equivalent to a line voltage (48V) is supplied to the telephone line 22. Therefore, both the facsimile 20 and the FAX modem circuit 24 are in the same electrical state in that both are connected through the telephone line 22.
In case of performing data transmission from the FAX modem circuit 24 to the facsimile machine 20, ringback signals which are supposed to be generated by a switchboard are outputted from the FAX modem circuit 24. Upon receiving the ringback signals, the facsimile machine 20 sends back an answering tone corresponding to the ringback signals. Thereafter, procedures for data transmission in accordance with the ITU-T recommendation can be performed between the FAX modem circuit 24 and the facsimile machine 20. In addition, the answering tone is outputted from the FAX modem circuit 24 when data transmission from the FAX modem circuit 24 to the facsimile machine 20 is performed. Then, the procedures for data transmission in accordance with the ITU-T recommendation can be performed between the FAX modem circuit 24 and the facsimile machine 20.
Thus, direct data transmission between the FAX modem circuit 24 and the facsimile machine 20 can be performed without utilizing the telephone line 22. Thus, the invention laid opened in the laid-open publication number Hei 2-218259 has a great value.